1. Field of the Invention
The invention relates to an error correction method for the transfer of word-wise arranged data, comprising the following steps:
a. receiving a succession of first numbers of data words in a first error encoder and adding to each first number of data words a first series of parity words on the basis of a first generator matrix of a first work correction code;
b. interleaving said first numbers of data words and first series of parity words by means of respective delay times which are all different within each first number and associated first series in order to form a succession of second numbers of words, each second number of words having a number of data words equal to said first number plus a number of check words equal to the number in a first series;
c. receiving a second number of words of said succession in a second error encoder and adding to said second number of words a second series of parity words on the basis of a second generator matrix of a second work correction code so as to form a third number of words;
d. word-by-word modulation of said third numbers of words serially linked in order to form channel words which satisfy, by way of added redundancy, predetermined upper limits and lower limits for the admissible intervals between directly successive signal transitions, said channel words being serially concatenated and pair-wise separated by merging bits which in combination with the channel words also satisfy said upper limits and lower limits in conjunction therewith;
e. demodulation of the channel words and merging bits after the transfer in order to reconstruct said third numbers of words;
f. receiving said third numbers of words, and from each third number reproducing, and if possible and necessary, correcting said second numbers of words, on the basis of the second parity check matrix associated with the second generator matrix;
g. deinterleaving said second numbers of words, followed by the reproducing therefrom, and if possible and necessary, correcting said first numbers of data words for a user on the basis of the first parity check matrix associated with the first generator matrix.
2. Description of the Prior Art
Part of a transfer with error correction as set forth above has already been disclosed in U.S. patent application Ser. No. 265,465 filed May 20, 1981, now abandoned, which Application is based on a Japanese Application No. 567608-80 in the name of Sony Corporation, Sinagawa-ku, Tokyo, Japan, and is incorporated herein by way of reference, although not by way of limitation. According to the prior art, within a second number of words, or within a third number of words, respective limited numbers of words can thus be corrected or a further limited number of words can be detected as being incorrect, said limited numbers being given by the minimum Hamming distance of the code taken over the words or symbols. This capability will be described in detail hereinafter. If the number of incorrect words within a second or third number of words is larger than the relevant admissible value, the error correction or the detection of incorrect words fails. When the error correction fails, either incorrect words are not corrected or words are incorrectly corrected, or both. If the error detection fails, either correct words are indicated as being incorrect or incorrect words are not indicated as being incorrect, or both. For completeness' sake it is mentioned that the prior art includes further interleaving steps before the first error encoding and between the second error encoding and the modulation. Furthermore, the modulation and demodulation has been described in British Patent Application No. 2083322 published Mar. 17, 1982. The modulation is a kind of coding for realizing a run-length-limited code; the transitions in the signal value are transitions from a channel bit having a first signal value to a channel bit having the second signal value.